Velocity selection in electron tubes



Patented Oct. 23, 1951 UNITED STATES PATENT OFFICE VELOCITY SELECTION IN ELECTRON TUBES Gardner L. Krieger and George A. Morton,

Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application June 28, 1946, Serial No. 67 9,928

Claims. l

v This invention relates to electron tubes having .means for selecting and utilizing electrons in accordance with their velocities. The invention will be described with reference to electron image tubes for directly viewing objects by radiant energy such as infra red and visible light energies, but this is merely an example and the principles of the invention are capable of application to many other electron devices.

It is an object of the invention to vary the velocity of the electrons proceeding from a tube .target in accordance with the image of an object projected thereon.

It is another object of the invention to provide an electron tube in which the electrons proceeding from the image of an object on the tube target are velocity selected for production of an image to be viewed.

.Other objects of the invention will appear in the following description, reference being had to the 'drawings, in which:

Figure 1 illustrates an electron tube in which the higher velocity electrons are selected for utilization at the uorescent screen.

Figure 2 illustrates an electron tube in which the lower velocity electrons are selected.

Figure 3 contains graphs showing velocities of .electrons emitted from elemental areas of a target.

Referring to Fig. 1 of the drawing, the viewing .tube consists of an evacuated envelope I of glass or other suitable material containing a target T :at one end and a fluorescent screen S at the other end. The target T differs from the usual target in that it comprises a body 2 adapted to ychange its resistance by heat, light, or other 'radiant energy focused thereon.

By way of example it will be assumed that the target will be used for thermal image effects. It may have either a negative or a positive coefficient of resistance, a negative coefcient being chosen for describing the operation. Glass is a good material to be used, but various others may be employed. To obtain a positive image the -high velocity electrons are utilized and the low velocity electrons rejected. The resistance body 2, such as glass, has a thin conducting coating 3, such as silver, for example, which is grounded to, say, the minus terminal of Athe voltage supply.l On the front of the target at 4 are small discrete areas of emissive material constituting the mosaic orpicture elements cap ableof` producing thermionic, p hoto-electric or secondary electron emission, as may be desired. Merely by way of example we have indicated a v2 rst source of radiant energy such as a heater coil H on the outside of the tube for heating the target for producing electron emission from the elements 4 substantially uniformly over the target. Alternatively, an appropriate heater may be placed inside the envelope I, if desired.

In an intermediate portion of the tube is placed a selector or control grid 5, which we employ for velocity selection of the electrons emitted by the target. Between the grid and the target are placed electrostatic ring electrodes 6 and 1. Between the grid and the fluorescent screen S are placed two additional ring electrodes 8 and 9. These ring electrodes are for accelerating the electrons toward the grid and the fluorescent screen, respectively. Electrostatic focusing may be used, but We have shown a coil I0 on the outside of the tube for producing electromagnetic focusing of the electrons, which operates in a well-known way.

Adjacent the target end of the tube may be placed a radiation focusing unit, generally designated as Il, which may contain appropriate lenses for imaging the thermal energy proceeding from the object to be viewed. This object may be considered as a second source of radiant energy. 'Ihe lenses may be made of rock salt and the adjacent end l2 may be made of an eiiicient heat transmitter, such as silver chloride. This can be sealed to the glass envelope to form a vacuum-tight joint. Various voltages may be applied to the electrodes of the tube, as will be understood by those skilled in the art, but We have indicated by way of example suitable voltages on the drawing, which may be adjustable above or below the values given.

To operate the tube with the assumptions made, with no thermal image on the target, current through heater H may be varied to adjust the temperature of the target to a value in the neighborhood of 40 C. or 50 C., at which temperature the electron current through the tube, that is, current flowing from target T to fluorescent screen S, will be in the order of 10-10 amps./cm.2 and the volt velocities of the emitted electrons are indicated by graph A of Fig. 3. The electron current will produce a voltage drop from the back to the front side of the target T. The voltage of selector grid 5 is then adjusted until it is sufficiently negative to cut off all, or substantially all, of the electron current through the tube, V1 being the critical volt velocity. The

emitted electrons of all velocities are then collected by the rings 6, 1 or other part of the tube. If now a, thermal or temperature image of an object be formed on the target, the temperature ofthe target body 2 will increase in proportion to the thermal energy received over its surface and the resistances of the plurality of paths to the picture areas will decrease accordingly. Thus, there will be a potential image produced over the emitting surface. The voltage drop in each of the paths through the target to the picture elements will decrease with the temperature increase of each path and the elemental areas 4 will become more negative with respect to the control grid 5, except those from areas with minimum or no image heat (dark areas). Graph B indicates the relation between the velocities of the areas receiving medium heat (gray areas). The curve B has the same form as curve A, but since the electrons from the gray areas have been emitted by more negative surfaces, the graph has been, in effect, moved past V1 and the number-of electrons represented grid from each picture element on the target il varies with the energy received from the imageV focused on the target. That is, there is intensity modulation. The electrons passing the selector vor grid 5 are accelerated and focused by elec- -trodes 8 and 9 to and on uorescent screeny S and produce thereon a picture of the object imaged on the target T.

If light, or near, or intermediate infrared radiation is used to image the object on the target, the resistance body may be made of materials such as activated cadmium selenide or lead sulphide, the resistance of which varies inversely with the radiation received. The conducting coating 3 may be transparent to the radiation used and the heat produced in the body 2'-, or it may absorb heat and transmit it to the body'2.

Instead of using a grid for selecting the electrons, we may use an electrode at the end of the'tube as an electron mirror and reect and utilize the lower velocity electrons the higher velocity electrons landing on such electrode. This is vshown in Fig. 2. To get a positive image the target body 2 would have a positive coeicient of resistance, which can be obtained by a composite structure combining materials with negative and positive coefficient of resistance the latter being chiefly metals but some materials like titanium oxide (TizOa) have a 'positive resistance coefficient below a critical thereon. Tov reflect the ultraviolet radiation onto the emissive particles 4, the metalfocusing elec'- trodes I5, I6 and l'I-may be Asand-blasted to give diffused reection of the energy to the target.

- The voltage of the mirror is such that the higher velocity electrons land on the mirror, while the lower velocity electrons are turned back and are focused on the fluorescent screen S where the image is produced. By way of example, we have given in this figure suitable voltages for the electrodes. I f Y l l In the embodiment of Fig. 2, curve A of Fig. 3 indicates the velocities of electrons emitted byr each picture element 4, with substantially no image energy thereon. The potential of the mirror 22 is adjusted so that substantially all electrons land thereon, the critical velocity being indicated by Vo. Electrons with velocities below this value cannot land. When a heat image, for example, is projected onto the target,

curve A indicates the velocity distribution for the dark areas and the relation to the critical volt velocity V0. Substantially no electrons from the dark elements reach the screen S. They have relatively high velocity'and land on electron mirror 32. In the gray areas, indicated by graph D, the electrons with volt velocities below Vo are reflected and accelerated to screen S. The number of medium velocity electrons thus received -by the screen S is given by VoQsV.. In the white areas, the electrons with velocities below Vo are likewise turned back by the mirror andare accelerated and focused on the 'screen S. The number of electrons received by the screen from these White elements is indicated by the area VOQ4V5 of graph E.

Various modications of the invention may be made without departing from the spirit thereof. Weclaimi' Y Y 1. An electron discharge device comprising, an

envelope, a target electrode mounted within saidV envelope, said target electrode formed of a material having a specific electrical resistance which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, an electron emissive material on an opposite surface of said target electrode, a fluorescent screen within said envelope, and a selector electrode mounted between said target electrode and said fluorescent screen, a rst source of radiant energy adjacent said target electrode for establishing a specific resistance between said conductive and said electron emissive coating, lead means connected ytoV said conductive coating for joining said coating to a rst potential, Aelectrode means Within said envelope for accelerating the electrons from said emissive coating toward said fluorescent screen, means for focusing additional radiation similar to that of said first source from a second source of radiant energy upon said target electrode for changing the specific resistance of said target electrode, and lead means connected to said selector electrode for joining said selector to a second potential for blocking electrons from those portions of the emissive target coating in contact with said target portions not subjected to radiations from said second source of energy.

2. An electron discharge device comprising, an envelope, a target electrode mounted -within said envelope, said target electrode formed of a material having a photoconductivity which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, an electron emissive mosaic on an op,- posite surface of said target electrode, a fluorescent screen within said-envelope, and a selector electrode mounted between said targetl electrode and said fluorescent. screen, a rstsource of raenergy adjacent said target electrode for establishing a specific conductivity through said photocondnctive target material and between said conductive coating and said electron emissive mosaic,J lead; means connected to said conductive coating for joining said coating to a iirst poten.- tial,. electrode means within said envelope for accelerating the electrons from said emissive mosaic toward; said uorescent screen, means for focusing additional radiation similar to that of said first source from a second source ofr radiant energy upon said target electrode for changing the specic resistance of said target electrode, and lead means connected to said selector electrode1 forl joining said selector to a second potential for blocking electrons from those portions of the emissive target mosaic in contact with` said target portions subjected to radiations from. said secondsource of energy.

- 3. An electron discharge device comprising, an envelope, a target electrode mounted within said envelope, said target electrode having a. body of glass having a specic electrode resistance which is afunction of radiant energy impinging thereon, a conductive coating on one surface of said glass target body, an electron emissive material on an opposite surface of said glass body, a fluorescent screen within said envelope, and a selector electrode mounted between said target electrode and said fluorescent screen, a rst Source of radiant energy adjacent said target electrode for establishing a specific resistance within. said glass body and between said conductive coating and said electron emissive material, lead means connected to said conductive coating for joining said coating to a rst potential, electrode means within said envelope for accelerating the electrons from said emissive target material toward said fluorescent screen, means for focusing additional radiation similar to that of said first source from a second source of radiant energy upon said target electrode for changing the speci'c resistance of said target electrode, and lead means connected to said selector electrode for joining said selector to a second potential for blocking electrons from those portions of the emissive target material in contact with said target portions not subjected to radiations from said second source of energy.

4. An electron discharge device comprising, an envelope, a target electrode mounted within said envelope,l said target electrode formed of a material having a photosensitivity which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, an electron emissive mosaic on an opposite surface of said target electrode, a uorescent screen within said envelope, and a selector electrode mounted between said target electrode and said fluorescent screen, a first source of radiant energy adjacent said target electrode for establishing a specific resistance within said photosensitive target and between said conductive coating and said electron emissive mosaic, lead means connected to said conductive coating for joining said coating to a source of potential, electrode means Within said envelope for accelerating the electrons from said emissive coating toward said fluorescent screen, means for focusing 'J additional radiation from a second source of radiant energy similar to that of said first source upon said target electrode for changing the specific resistance of said target electrode, and lead Cil joiningysaid' selector to a second source, of potentiali for blocking electrons from those portionsv of the emissivetarget coating. in contact with said target portions subjected toi radiations from said secondrsource of energy.

5. An electron discharge device comprising, an envelope, a target electrode; mounted within said envelope, said target electrode. having a specific electrical resistance which. is a. function of ra,- diant energy impinging thereon, a conductive coating on one surface of said targetv electrode, an electronA emissive mosaic on an` opposite; surface of said target electrode, a uorescent screen within said envelope, and an electron pervious mesh electrode mounted between said target electrode and said iiuorescent screen, a first source of radiant energy adjacent said target electrode for establishing a speciiic resistancewithin-said target. electrode and. between said conductive coating va-nd said electronemissive mosaic, lead means connected to said conductive coating for joining said coating to a first potential, electrode means within said envelope foracceleratring the electrons from said emissivemosaic toward said fluorescent screen, means for focusing additional radiation similar to that of'said first-source from a second source of radiant energy upon said target electrode for changing the speciiic resistance of said target electrode, and lead means connected to said electron pervious mesh for joining said mesh to a second potential for blocking electrons from those portions of the emissive target mosaic in contact with said target portions not subjected to radiations from said second source of energy. l

6. An electron discharge device comprising. an envelope, a target electrode mounted withinL said envelope, said target electrode having a. specific electrical resistance which is a function of radiant energy impinging thereon, a conductive coating lon. one surface of said target electrode, an electron emissive mosaic on an opposite surface of said target electrode, a fluorescent screen Within said envelope, and an electron mirror electrode mounted between said target'electrode and said uorescent screen, a first source of radiant energy adjacent said target electrode for establishing a specific resistance within saidtarget electrode and between Asaid conductive and said electron-emissive mosaic, lead means connected to said conductive coating for joining said coating to a first potential, electrodemeans within said envelope for accelerating the electrons from said emissive mosaic toward said iiuorescent screen, means for focusing additional means connected to said selector electrode for' zo radiation similar to that of said first source from a second source of radiant energy upon said` target electrode for changing the specic resistance of said target electrode, and leadmeans con,- nected to said electron mirroi-.electrode forfjoinfing said electron mirror to a second potential for blocking electrons from those portions of 1 the emissive target mosaic in contact with said target portions not subjected to radiations from said second source of energy.

7. An electron discharge device comprising, an envelope, an electron emitting electrode mounted within said envelope and formed of a material having a specic electrical resistance which is a function of a radiant energy impinging thereon, a conductive coating on one surface of said electron emitting electrode, an electron emissive coating on an opposite surface thereof, an electron collecting screen electrode mounted within said envelope transversely to thepaths of electrons emitted from said target electrode, and a selector electrode mounted within said envelope intercepting said electron paths, a first source of radiant energy adjacent said target electrode for establishing a specic resistance between said conductive and electron emissive target coatings, lead means connected to said conductive coating for joining said coating toa first potential, electrode means within said envelope for accelerating the electrons from said emissive coating toward said collecting screen electrode, means for focusing additional radiation similar to that of said rst source from a second source of radiant energy upon said target electrode for changing the specific resistance of said target electrode and lead means connected to said selector electrode Vfor joining .said selector electrode to a second potential for blocking electrons from those portions' of the emissive target coating inV contact 'with target portions subjected to radiations from 'said second source of energy.

8. An electron tube device comprising, an envelope, a target electrode mounted within said envelope, said target electrode formed ofa radiation sensitive material having a specific electrical resistance which is a function of radiant energy impinging thereon, a conductive electrode in contact with one surface of one target electrode, an electron emissive material on the other surface of said target electrode, 'means-for initiating an electron emission vfrom said electron emissive target material, a collector screen electrode within said envelope'for 'said electron emission, a selector electrode mounted between said collector screen electrode and said target electrode, lead means connected to said conductive electrode for joining said conductive electrode to a first potential, electrode means within said envelope for accelerating electrons from said emissive target coating towards said collector screen electrode, means for focusing radiation from a source of Aradiant Venergy upon said target electrode for changing the specic resistance of said target material, and lead means connected to said selector electrode for joining said selector to a second potential for blocking electrons from those portions of the emissive target coating in contact with the target portion not subjected to radiations from said source of radiant energy.

9. An electron tube device comprising, an envelope, a target electrode mounted within said envelope, said target electrode formed of a radiation sensitive material having a specific electrical rel rsistance which is a function of radiant energy impinging thereon, a conductive coating on one surface of said target electrode, a photosensitive material on an opposite surface of said target electrode, means for initiating emission from said photosensitive target material, a collector screen electrode within said envelope for said photoemission, a selector electrode mounted between said collector screen electrode and said target electrode, lead means connected to said conductive target coating for joining said coating to a rst potential, electrode means within said envelope for accelerating electrons from said photoemissive target material toward said collector screen electrode, means for focusing radiation from a source of radiant energy upon said target electrode for changing the specific resistance of vsaid target material, and lead means connected ing on one surface of said'target electrode, an.`

electron sensitive material on an opposite surface of said target electrode, means for initiating emission from said electron emissive target-imaterial, a collector screen electrode Within said envelope for said photoemission, a selector electrode mounted between said collector screen electrode and said target electrode, lead means connected to said conductive targetcoating for' joining said coating to a vrst potential, electrode 'means within said envelope for accelerating electrons from said emissive target coating toward said collector screen electrode, means for focus` ing radiation from a source of radiant energy upon said glass target electrode for changing the specic resistance of said target material, vand lead means connected to said selector electrode for joining said selector to a second potential for blocking the electrons from those portions of the emissive target coating in contact with glass target portions subjected to radiation fromV said source of radiant energy.

GARDNER L. KRIEGER. GEORGE A. MORTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Date v Name i 2,021,907 Zworykin Nov. 26, 1935V 2,163,787 Henneberg et al. June 27, 1939 2,189,321 Morton l Feb. 6, 1940 2,264,709 'Nicoll Dec. 2, 1941 2,306,881 Heimann et al. Dec. 29, 1942 FOREIGN PATENTS Number Country Date 812,946 France Feb. 15, 1936 478,238 Great Britain Jan. 13, 1938 

